This invention relates generally to aircraft capable of combined rotary wing and fixed wing flight and, more particularly, to apparatus for controlling movement of the rotor blades of such aircraft.
Rotor/wing aircraft such as the aircraft disclosed in U.S. Pat. No. 5,454,530 titled "Canard Rotor/Wing" are capable of operation in both a helicopter and a fixed-wing mode of flight. In order to achieve this dual mode flight, a rotor/wing aircraft is equipped with a rotating hub, similar to the rotating hub of a helicopter, to which are attached a plurality of rotor blades extending radially outward from the hub. In the first flight regime the hub and rotor blades are rotated in a manner similar to that of a helicopter. This enables the aircraft to move vertically, hover, and fly translationally at relatively slow speeds. In the second flight regime, the rotor is locked with the rotor blades positioned to operate as fixed wings, thereby enabling the aircraft to fly at relatively high speeds configured as a conventional fixed-wing aircraft.
In order to enable a rotor/wing aircraft to operate in the helicopter mode, the blades of the rotor/wing must be free to rotate about their respective pitch axes in response to the control inputs. As with a conventional helicopter, the longitudinal and lateral rotor blade cyclic pitch control as well as the average rotor blade pitch (collective) are transmitted the rotor blades by means of a rotor blade swashplate mechanism. Pilot control inputs are translated into elevation and tilt angle of the swashplate which are transmitted to the rotor blades by means of pitch links attached to the leading edges of the blades.
For the rotor/wing aircraft to operate in fixed wing mode, however, the rotor blades must be locked into a rigid assembly. The relatively low stiffness of the rotor swashplate mechanism and its actuators and the potential for brinelling of the loaded static rolling bearings of the rotor swashplate mechanism preclude effective use of the rotor swashplate mechanism as a means for securing the rotor blades for fixed wing flight. Accordingly, it is desirable to provide an independent, rigid mechanism for securing rotor blades about their pitch axes during fixed wing flight.